The objective of this research is delineation of biochemical and genetic mechanisms which regulate the rate of human purine nucleotide synthesis and coordinate the activities of this and other biosynthetic pathways. Several discrete hereditary enzyme abnormalities have been identified which account for the excessive purine production of a small proportion of patients with gout. Studies of these enzyme defects have contributed to current concepts of the biochemical control of purine nucleotide synthesis, emphasizing the importance of the antagonistic interaction between the regulatory substrate 5-phosphoribosyl 1-pyrophosphate (PRPP) and inhibitory purine nucleotide products. The frequency with which kinetic variation within known enzyme abnormalities contributes to the purine overproduction of additional patients with gout will be evaluated and an attempt will be made to identify and characterize other enzyme aberrations among such patients. The delineation of additional regulatory determinants will also be the aim of studies of (1) the effects of chemical agents on human purine metabolism in vivo and (2) the importance of rates of generation of pentose phosphates, particularly ribose-5-P, in determining PRPP synthesis in human fibroblasts in culture. Synthesis of PRPP is catalyzed by the enzyme PRPP synthetase, the structure and activity of which is subject to modification by a number of effector compounds. Determinants of the structure, activity and amount of PRPP synthetase will be investigated in purified enzyme preparations and in cultured cells derived from normal individuals and from patients with mutant forms of PRPP synthetase which result in excessive enzyme activity, increased PRPP synthesis and purine overproduction. The potential significance of the close linkage on the human X-chromosome of the structural loci for PRPP synthetase and hypoxanthin-quanine phosphoribosyltransferase will be evaluated in studies of PRPP synthetase messenger RNA. The role of PRPP in the regulation of the rate of pyrimidine nucleotide synthesis and its coordination with purine nucleotide synthetic rate will be evaluated in cultured fibroblasts and lymphoblasts utilizing normal cells and cells containing specific genetic alterations in enzymes of purine and pyrimidine metabolism.